What is the molecular formula for butanoic acid?

Butanoic acid, also known as butyric acid, is a carboxylic acid with a four-carbon backbone. Its structure comprises a straight chain of four carbon atoms (C4), with a carboxyl group (-COOH) attached to one end. To derive the molecular formula, we can break it down as follows:

1. The carbon chain contributes 4 carbon atoms.

2. Each carbon is typically bonded to enough hydrogen atoms to fulfill the tetravalence of carbon. For butanoic acid, the general formula for a saturated fatty acid is CₙH₂ₙ₊₁COOH, where n is the number of carbon atoms in the chain.

3. For butanoic acid (n = 4), the formula can be deduced as C4H9 (from the chain) + COOH (the carboxyl group), which adds one carbon atom, two oxygen atoms, and one hydrogen atom.

Thus, the complete molecular formula is C4 (from the carbon chain) + COOH, resulting in C4H8O2, matching the correct answer. This understanding highlights the structural aspect of butanoic acid that confirms its molecular composition.